Ofloxacin [i.e., (.+-.)-9-fluoro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-2,3-dihydro-7H- pyrido[1,2,3de][1,4]benzoxazine-6-carboxylic acid] is an excellent antimicrobial agent as disclosed in U.S. Pat. No. 4,382,892 and has been chiefly administered as an oral preparation as described, e.g., Japanese Patent Application (OPI) No. 46986/82 (the term "OPI" as used herein means "unexamined published Japanese patent application"). In particular, one of the optical isomers of Ofloxacin, S-(-)-9-fluoro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-2,3-dihydro-7H-p yrido[1,2,3de][1,4]benzoxazine-6-carboxylic acid (hereinafter referred to as S-compound) described in U.S. patent application Ser. No. 876,623 filed June 20, 1986, exhibits potential antimicrobial activities and is expected for use as various pharmaceuticals as reported in Antimicrobial Agent & Chemotherapy, Vol. 29, 163-164 (1986)